During the past two years we have developed methods for isolating large numbers of idiotype-specific suppressor T cells. We are now in the process of attempting to isolate a soluble suppressor factor from such cells. Preliminary work is promising but complete suppression has not yet been attained. We will therefore continue our studies, attempting to generate large numbers of specific suppressor T cells, and to isolate suppressive factors from the membrane or cytoplasm of such cells. In another line of investigation, we will provide specifically purified anti-Ar antibodies to Dr. J.D. Capra, who is carrying out amino acid sequence studies on their heavy chains. We will also provide him with heavy chains from hybridoma products which carry the cross-reactive idiotype and other closely related idiotypes which we have found to be present in immune sera. In a third line of investigation, we will extend our studies indicating that four strains, which synthesize light chains possessing a unique polypeptide marker, fail to provide the necessary light chains for the production of an idiotype associated with anti-phenylarsonate antibodies in A/J mice. The generality of this phenomenon will be determined by extending this work to other idiotypes characteristic of particular strains of mice. In each case the second strain used in the mating study, will be one of the four strains which is characterized by the unusual light chain marker.